add bomberman example

Cargo.toml

@@ -35,8 +35,12 @@ name = "non_interactive_fheuint8"
 path = "./examples/non_interactive_fheuint8.rs"
 required-features = ["non_interactive_mp"]
 
-
 [[example]]
 name = "meeting_friends"
 path = "./examples/meeting_friends.rs"
+required-features = ["non_interactive_mp"]
+
+[[example]]
+name = "bomberman"
+path = "./examples/bomberman.rs"
 required-features = ["non_interactive_mp"]

examples/bomberman.rs

@@ -0,0 +1,163 @@
+use std::fmt::Debug;
+
+use bin_rs::*;
+use itertools::Itertools;
+use rand::{thread_rng, Rng, RngCore};
+
+struct Coordinates<T>(T, T);
+impl<T> Coordinates<T> {
+    fn new(x: T, y: T) -> Self {
+        Coordinates(x, y)
+    }
+    fn x(&self) -> &T {
+        &self.0
+    }
+
+    fn y(&self) -> &T {
+        &self.1
+    }
+}
+
+impl<T> Debug for Coordinates<T>
+where
+    T: Debug,
+{
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        f.debug_struct("Coordinates")
+            .field("x", self.x())
+            .field("y", self.y())
+            .finish()
+    }
+}
+
+fn coordinates_is_equal(a: &Coordinates<FheUint8>, b: &Coordinates<FheUint8>) -> FheBool {
+    &(a.x().eq(b.x())) & &(a.y().eq(b.y()))
+}
+
+fn traverse_map(p0: &[Coordinates<FheUint8>], bomb_coords: &[Coordinates<FheUint8>]) -> FheBool {
+    // First move
+    let mut out = coordinates_is_equal(&p0[0], &bomb_coords[0]);
+    bomb_coords.iter().skip(1).for_each(|b_coord| {
+        out |= coordinates_is_equal(&p0[0], &b_coord);
+    });
+
+    // rest of the moves
+    p0.iter().skip(1).for_each(|m_coord| {
+        bomb_coords.iter().for_each(|b_coord| {
+            out |= coordinates_is_equal(m_coord, b_coord);
+        });
+    });
+
+    out
+}
+
+// Do you recall bomberman? It's an interesting game where the bomberman has to
+// cross the map without stepping on strategically placed bombs all across the
+// map. Below we implement a very basic prototype of bomberman with 4 players.
+//
+// The map has 256 tiles with bottom left-most tile labelled with coordinate
+// (0,0) and top right-most tile labelled with coordinate (255, 255). There are
+// 4 players: Player 0, Player 1, Player 2, Player 3. Player 0's task is to walk
+// across the map with fixed no. of moves while preventing itself from stepping
+// on any of the bombs placed across the map by Player 1, 2, and 3.
+//
+// The twist is that Player 0's moves and the locations of bombs placed by other
+// players are encrypted. Player 0 moves across the map in encrypted domain.
+// Only a boolean output indicating whether player 0 survived after all the
+// moves or killed itself by stepping onto a bomb is revealed at the end. If
+// player 0 survives, Player 1, 2, 3 never learn what moves did it make. If
+// player 0 kills itself by stepping onto a bomb, it only learns that bomb was
+// placed on one coordinates it moved to. Moreover, Player 1, 2, 3 never learn
+// about locations of each other bombs or even whose bomb killed Player 1.
+fn main() {
+    set_parameter_set(ParameterSelector::NonInteractiveLTE4Party);
+
+    // set application's common reference seed
+    let mut seed = [0; 32];
+    thread_rng().fill_bytes(&mut seed);
+    set_common_reference_seed(seed);
+
+    let no_of_parties = 4;
+
+    // Client side //
+
+    let cks = (0..no_of_parties).map(|_| gen_client_key()).collect_vec();
+
+    let server_key_shares = cks
+        .iter()
+        .enumerate()
+        .map(|(index, k)| gen_server_key_share(index, no_of_parties, k))
+        .collect_vec();
+
+    // encrypt inputs
+    let no_of_moves = 10;
+    let player_0_moves = (0..no_of_moves)
+        .map(|_| Coordinates::new(thread_rng().gen::<u8>(), thread_rng().gen()))
+        .collect_vec();
+    let player_1_bomb = Coordinates::new(thread_rng().gen::<u8>(), thread_rng().gen());
+    let player_2_bomb = Coordinates::new(thread_rng().gen::<u8>(), thread_rng().gen());
+    let player_3_bomb = Coordinates::new(thread_rng().gen::<u8>(), thread_rng().gen());
+
+    println!("P0 move coordinates: {:?}", &player_0_moves);
+    println!("P1 bomb coordinate : {:?}", &player_1_bomb);
+    println!("P2 bomb coordinate : {:?}", &player_2_bomb);
+    println!("P3 bomb coordinate : {:?}", &player_3_bomb);
+
+    // Al playes encrypt their private inputs
+    let player_0_enc = cks[0].encrypt(
+        player_0_moves
+            .iter()
+            .flat_map(|c| vec![*c.x(), *c.y()])
+            .collect_vec()
+            .as_slice(),
+    );
+    let player_1_enc = cks[1].encrypt(vec![*player_1_bomb.x(), *player_1_bomb.y()].as_slice());
+    let player_2_enc = cks[2].encrypt(vec![*player_2_bomb.x(), *player_2_bomb.y()].as_slice());
+    let player_3_enc = cks[3].encrypt(vec![*player_3_bomb.x(), *player_3_bomb.y()].as_slice());
+
+    // All player upload the encrypted inputs and server key shates to the server
+
+    // Server side //
+
+    let server_key = aggregate_server_key_shares(&server_key_shares);
+    server_key.set_server_key();
+
+    // server parses all player inputs
+    let player_0_moves_enc = {
+        let c = player_0_enc.unseed::<Vec<Vec<u64>>>().key_switch(0);
+        (0..no_of_moves)
+            .map(|i| Coordinates::new(c.extract(2 * i), c.extract(i * 2 + 1)))
+            .collect_vec()
+    };
+    let player_1_bomb_enc = {
+        let c = player_1_enc.unseed::<Vec<Vec<u64>>>().key_switch(1);
+        Coordinates::new(c.extract(0), c.extract(1))
+    };
+    let player_2_bomb_enc = {
+        let c = player_2_enc.unseed::<Vec<Vec<u64>>>().key_switch(2);
+        Coordinates::new(c.extract(0), c.extract(1))
+    };
+    let player_3_bomb_enc = {
+        let c = player_3_enc.unseed::<Vec<Vec<u64>>>().key_switch(3);
+        Coordinates::new(c.extract(0), c.extract(1))
+    };
+
+    // run the game
+    let player_0_dead_ct = traverse_map(
+        &player_0_moves_enc,
+        &vec![player_1_bomb_enc, player_2_bomb_enc, player_3_bomb_enc],
+    );
+
+    // All players generate decryption shares
+    let decryption_shares = cks
+        .iter()
+        .map(|k| k.gen_decryption_share(&player_0_dead_ct))
+        .collect_vec();
+    let player_0_dead = cks[0].aggregate_decryption_shares(&player_0_dead_ct, &decryption_shares);
+
+    if player_0_dead {
+        println!("Oops! Player 0 dead");
+    } else {
+        println!("Wohoo! Player 0 survived");
+    }
+}

src/bool/mp_api.rs

@@ -554,7 +554,8 @@ mod tests {
                             assert_eq!(
                                 m0_plus_m1,
                                 m0.wrapping_add(m1),
-                                "Expected {} but got {m0_plus_m1} for {i}+{j}",
+                                "Expected {} but got {m0_plus_m1} for
+                        {i}+{j}",
                                 m0.wrapping_add(m1)
                             );
                         }
@@ -565,7 +566,8 @@ mod tests {
                             assert_eq!(
                                 m0_sub_m1,
                                 m0.wrapping_sub(m1),
-                                "Expected {} but got {m0_sub_m1} for {i}-{j}",
+                                "Expected {} but got {m0_sub_m1} for
+                        {i}-{j}",
                                 m0.wrapping_sub(m1)
                             );
                         }
@@ -591,22 +593,26 @@ mod tests {
                                 let (q, r) = i.div_rem_euclid(&j);
                                 assert_eq!(
                                     m_quotient, q,
-                                    "Expected {} but got {m_quotient} for {i}/{j}",
+                                    "Expected {} but got {m_quotient} for
+                    {i}/{j}",
                                     q
                                 );
                                 assert_eq!(
                                     m_remainder, r,
-                                    "Expected {} but got {m_remainder} for {i}%{j}",
+                                    "Expected {} but got {m_remainder} for
+                    {i}%{j}",
                                     r
                                 );
                             } else {
                                 assert_eq!(
                                     m_quotient, 255,
-                                    "Expected 255 but got {m_quotient}. Case div by zero"
+                                    "Expected 255 but got {m_quotient}. Case
+                    div by zero"
                                 );
                                 assert_eq!(
                                     m_remainder, i,
-                                    "Expected {i} but got {m_remainder}. Case div by zero"
+                                    "Expected {i} but got {m_remainder}. Case
+                    div by zero"
                                 );
 
                                 let div_by_zero = ck.decrypt(&div_zero_error_flag().unwrap());

src/shortint/mod.rs

@@ -20,15 +20,32 @@ pub fn div_zero_error_flag() -> Option {
 mod frontend {
     use super::ops::{
         arbitrary_bit_adder, arbitrary_bit_division_for_quotient_and_rem, arbitrary_bit_subtractor,
-        eight_bit_mul,
+        eight_bit_mul, is_zero,
     };
     use crate::utils::{Global, WithLocal};
 
     use super::*;
 
-    mod arithetic {
+    /// Set Div by Zero flag after each divison. Div by zero flag is set to true
+    /// if either 1 of the division executed in circuit evaluation has
+    /// denominator set to 0.
+    fn set_div_by_zero_flag(denominator: &FheUint8) {
+        {
+            BoolEvaluator::with_local_mut(|e| {
+                let key = RuntimeServerKey::global();
+                let is_zero = is_zero(e, denominator.data(), key);
+                DIV_ZERO_ERROR.with_borrow_mut(|before_is_zero| {
+                    if before_is_zero.is_none() {
+                        *before_is_zero = Some(FheBool { data: is_zero });
+                    } else {
+                        e.or_inplace(before_is_zero.as_mut().unwrap().data_mut(), &is_zero, key);
+                    }
+                });
+            })
+        }
+    }
 
-        use ops::is_zero;
+    mod arithetic {
 
         use super::*;
         use std::ops::{Add, AddAssign, Div, Mul, Rem, Sub};
@@ -76,13 +93,12 @@ mod frontend {
         impl Div<&FheUint8> for &FheUint8 {
             type Output = FheUint8;
             fn div(self, rhs: &FheUint8) -> Self::Output {
+                // set div by 0 error flag
+                set_div_by_zero_flag(rhs);
+
                 BoolEvaluator::with_local_mut(|e| {
                     let key = RuntimeServerKey::global();
 
-                    // set div by 0 error flag
-                    let is_zero = is_zero(e, rhs.data(), key);
-                    DIV_ZERO_ERROR.set(Some(FheBool { data: is_zero }));
-
                     let (quotient, _) = arbitrary_bit_division_for_quotient_and_rem(
                         e,
                         self.data(),
@@ -141,13 +157,12 @@ mod frontend {
             }
 
             pub fn div_rem(&self, rhs: &FheUint8) -> (FheUint8, FheUint8) {
+                // set div by 0 error flag
+                set_div_by_zero_flag(rhs);
+
                 BoolEvaluator::with_local_mut(|e| {
                     let key = RuntimeServerKey::global();
 
-                    // set div by 0 error flag
-                    let is_zero = is_zero(e, rhs.data(), key);
-                    DIV_ZERO_ERROR.set(Some(FheBool { data: is_zero }));
-
                     let (quotient, remainder) = arbitrary_bit_division_for_quotient_and_rem(
                         e,
                         self.data(),